Brush bristles

ABSTRACT

Paint brush bristles formed from polybutylene-1,4-terephthalate exhibiting superior bend recovery and initial modulus of elasticity in flex as well as in paint solvents, satisfactory temperature dependence of modulus and amenability to flagging and tipping.

v United States Patent 1151 3,706,1 1 1 Curtin et al. 45 Dec, 19, 1972BRUSH BRISTLES [56] References Cited [72] Inventors: Dennis EdwardCnrtin, Parkersburg UNITED STATES PATENTS W. Va.; John Edward Hansen,Wilmington, DeL 2,292,905 8/1942 Smlth ..15/159 R 2,433,325 12/1947Slaughter ..161/179 [73] Ass1gnee: EJ. du Pont de Nemours and Com-2,465,319 3/1949 Whinfield et al.. ..161/172 pany, Wilmington, Del.2,615,784 10/1952 McClellan ..8/151 3,295,156 1/1967 Brant ..15/159 R[22] 1970 3,402,416 9/1968 Shaw et a1. ....l6l/l79 [21] App], No,;66,145 3,405,098 10/1968 Heighton et a1. ......260/75 3,344,457 10/1967Grobert ..15/159 A Related US. Application Data 7 [60] Division of Ser.No. 785,390, Dec. 19, 1968, abanf 'f f Hume doned, and a continuation ofSer. No. 66,661, Aug. Assistant Exammer-Lorrame Kendall 24, 1970,abandoned. Attorneywilliam A. Hoffman [52] US. Cl. ..15/159 A, 15/159 R,161/177, [57] ABSTRACT 161/179, 260/75 R, 264/210 F, 264/290 '1' [511111.01. ......A46b 1/00, A46d 1/00 brush bnsfles fmmed fmmPdybutyleneJA' f R, A; terephthalate exhibiting superior bend recoveryand 260/75 R initial modulus of elasticity in flex as well as in paintsolvents, satisfactory temperature dependence of modulus and amenabilityto flagging and tipping.

8 Claims, No Drawings BRUSH BRISTLES This is a division of applicationSer. No. 785,390 filed on Dec. 19, 1968 by Dennis Edward Curtin and JohnEdward Hansen, now abandoned and refiled as a continuation applicationSer. No. 66,661 on Aug. 24, 1970, now abandoned.

BACKGROUND OF THE INVENTION In the past, paint brush bristles have beenmade from natural bristle and from various synthetic resins. The betterpaint brush bristles have been formed from polyamides of whichpoly(hexamethylene sebacamide) is generally regarded as the best, due toits tensile modulus, bend recover/ and amenability to flagging andtipping. These bristles suffer from a general loss ofphysical'properties when used in conjunction with water base paints suchas the common latex wall paints and house paints as well as when used inconjunction with alcohol base coatings such as shellac, because thewater or alcohol dissolve in and soften or plasticize the bristle.

In the past, polyesters have been regarded as unsatisfactory for use informing paint brush bristles. The common polyester is poly(ethyleneterephthalate) which is unsatisfactory for use in forming paint brushbristles due to poor bend recovery, too high a modulus (bristles are toostiff), poor amenability to tipping and bad amenability to flagging.Other polyesters based on terephthalic acid have been found to beunsatisfactory for forming paint brush bristles. Poly(propyleneterephthalate) is unsatisfactory for use in forming paint invention, thetapered filament take-off device such as described in U.S. Pat. No.2,4l8,492 is used to produce tapered filament from the extruder prior toorienting. When forming such a tapered filament, the draw or orientationratio of the filament at the base of-each bristle should be from about3.5 to 4.5)( while the draw ratio of the tip should be from 3.5 to about5.5X. The diameter of the tip of such a tapered filament prior totipping preferably is from 0.5 to 0.75 times the diameter of the base ofthe bristle. Thus, in the case of tapered bristle the maximum diameterof the bristle may vary from 6 to 20 mils and the minimum diameter mayvary from 3 to 15 mils. The drawing operation may be carried out at from25 to 100 C in a liquid such as water, or 300 to 400 C in a gas such asair. the preferred temperature for use with a liquid bath is. from 70 to90 C. This heating may readily be carried out by means of electricheaters by blowing a heated gas over the filament, or by passing. thefilament through a heated liquid bath.

The filament preferably is heat set after drawing for good bendrecovery. While the heat setting operation may be carried outwith orwithout the application of tension, it is preferred to allow thefilament to relax in length from 5 to 15 percent during the heat settingbrush bristles due to too low 'a modulus (bristles are not stiffenough), poor processability of the filaments due to excessive shrinkageduring heat setting, which causes an excessive number of breaks, and badamenability to flagging. Poly(pentylene terephthalate) has been foundnot to be spinnable into bristle filaments. Poly(hexylene terephthalate)is unsatisfactory for use in forming paint brush bristles because ofpoor retention of modulus (stiffness or modulus of elasticity in flex)in several paint solvents and a substantial change in modulus in thetemperature range typically experienced in painting (2030 C).

SUMMARY OF THE INVENTION It has now been found that poly(butylene-l,4-terephthalate) is unique among the polyesters based on terephthalic acidin having the balance of properties,

i.e., excellent bend recovery, satisfactory initial modulus and wetmodulus in paint solvents, excellent ease of processability intofilaments, satisfactory temperature dependence of modulus, along withexcellent amenability to flagging and satisfactory amenability totipping. Y

In carrying out the present invention, a filament of from 6 to 40 milsdiameter is spun or extruded from poly(butylene-l,4-terephthalate)having an inherent viscosity of from 0.5 to 1.5 (as measured from a 0.5g solution in 100 ml of 40/60 tetrachloroethane/phenol). The filament isthen oriented by drawing from about 3.5 to about 5.5 times its originallength. The conventional slow-fast roll arrangement is suitable fororienting the filament. A single drawing stage is suitable, although atwo or three stage drawing operation can be used if desired. In anespecially preferred aspect of the operatiomThis relaxation during heatsetting generally results in improved straightness of the filament,although relaxation is not always needed to achieve adequatestraightness. The heat setting can be carried out either in a gas suchas by blowing hot air over the filament, or in a liquid bath such as bypassing the filament through a bath of oil. The filament should remainin the heat setting stage for from 30 to seconds in a gas, or from about2 to 10 seconds in a liquid bath. Temperatures of from 150 to 200 C aresuitable for the heat setting operation when using a gas, andtemperatures of from to 200 C when using a liquid bath.

The filaments are then cut to length to form individual bristles, whichare gathered into bundles of from about 1 to 2 inches in diameter to betipped and flagged. Conventional tipping and flagging apparatus such asdescribed in U.S. Pat. Nos. 2,697,009 and 2,911,761, is suitable forthis operation. Preferably, the tipping is performed on a wet abrasivewheel using a mixture of water and a lubricant such as Sulfo 5000 madeby Sulfo, Inc., as a coolant and a tipping aid. Bundles of untippedfilaments (all of one length) are placed in chucks, and the tips of thefilaments are passed over a series of abrasive wheels to grindapproximately the end three-eights inch of the tip of each filament to afine point.

The flagging operation can be performed by passing a bundle of thetipped bristles over a series of rotating knives in which case most ofthe bristles have a bushy tip having about four to 10 fuzzy flags. It ispreferable to wet the bundles before flagging with a solution such as amixture of water and a lubricant such as used in the tipping operation.The conventional flagging machines presently used commercially forflagging polyamide and other paint brush bristles are suitable for usein the present invention. Optionally, the bristles can be microflagged.This is most readily done by making up a brush of tipped but not flaggedbristles. The tips of the bristles are then beaten by rods or similarmeans which means have small projections or ridges such as threads on ascrew. Microflagged bristles generally have to 20 micro-hair divisionsat the tip.

Paint brush bristles made from poly(butylene-l,4-

terephthalate) and processed in the above manner exhibit fine slendertips and strong multiend flags which are unobtainable with conventionalpolyester filaments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE I Poly(butylene-l,4-terephthalate)flake having an inherent viscosity of 0.7.as measuredfrom a 0.5 g percent solution in 100 ml of 60 percent phenol and 40percent tetrachloroethane is dried in an oven at 100 C for 20 hours witha nitrogen sweep and an additional 24 hours I at 160 C with a nitrogensweep to dry the flake. The

flake is then charged to a 1 /4 inch single screw extruder arranged withits discharge coupled directly to the intake of a metering gear pump.The melted polymer in the extruder is maintained at 255 C. The gear pumpoperated at a cyclically varying surface speed as described in U.S. Pat.No. 2,418,492, which results in a correspondingly varying stranddiameter of from 16 mils minimum diameter to 24 mils diameter maximumwith approximately 2% inches repeat distance between pointsof maximumand minimum diameter. These tapered filaments are drawn from 4 to 4.2Xwith a conventional slow roll-fast roll" arrangement using a shorttubular furnace maintained at 350 to 400 C air temperature between theslow roll and fast roll as a draw assist.

The filament is wound up on a spool and then in a second operation thefilament is passed through a hot air conditioning oven maintained at 170to 180 C with a residence in the oven of about 40 seconds. The filamentis permitted to relax in length 10 percent as it passes through the ovento improve the straightness of the filament when out and bundled asbristle. The heat setting also serves to maximize the bend recovery ofthe final product.

After spinning, drawing, and heat setting as a continuous lengthfilament, the filament is cut at each point of minimum diameter and thepieces, which are at least twice the length of the desired product, inthis case about 10 inches long, 12 to 8 mil maximum to minimumdiameters, gathered into double taper bundles. These are then trimmed tosingle taper bundles of 3% to 4 inch lengths. The bristles are thentipped by contacting the end one-half to five-eights inch of about 1%inch diameter bundles of filaments, using a multiple pass, with 10-inchdiameter, l-inch width, No. A 46-05Vl type grinding wheels while holdingthe filaments in a chuck which revolves continuously to expose all sidesof the filaments to the grinding wheels. During this operation anaqueous solution containing 2 percent Sulfo 5000 lubricant iscontinuously sprayed onto the bundles and grinding wheels to act as acoolant and tipping aid.

The bristles are then flagged by passing the bundles of the tippedbristles over a series of 48, 3-inch diameter rotating pointed blades ina Baer flagging machine.

This operation splits the tips of nearly 'all of the bristles into fouror more parts (flags). The bristles are wetted with the same aqueoussolution used in the tipping operation. The depth of flagging canreadily be varied from one-eighth to one-fourth inch by adjusting theinterface between the knives and the bundle tips. The choice of flagdepth is governed by the bristles length and the type of brush desired.These bristles can be splitinto a distinctly greater number of flagsthan has been found possible using similarprocesses with polyamide orpoly(ethylene terephthalate) bristles.

The bristles are then madeup into a 4-inch wide, 1- inch thick paintbrush containing grams of filament of which 70 percent are flagged to adepth of between three-sixteenths and one-fourth inch. When tested usingan oil base paint containing 35 percent vehicle and 65 percent pigmentof which the vehicle composition is 3 percent drier, 70 percentaliphatic hydrocarbons and 27 percent soya alkyd resin, and the pigmentcontains 21 percent titanium dioxide, 3 percent zinc oxide, 74 percentcalcium carbonate and 2 percent diatomaceous silica, the brush exhibitsa dump of 4.5 grams, a paint release" of 22.9 grams, .and a coverage ofsquare inches.

As used herein, paint release is the average weight of paint transferredfrom a dipped brush to a surface during painting by the brush-in astandard apparatus. The brush is prepared for the test by soaking inmineral spirits for 24:4 hours, and allowed to air dry for 24:4 hours.The bristle is then combed four times, starting at the heel and strokingforwardv to the tip.'The brush is then conditioned for 24:4 hours at23:2 C and 50:5 percent R.l-l. The viscosity of the paint used ismeasured to obtain uniformity when comparative tests on various brushesare made. The brush is mounted in the holder of a painting machine sothe tip would extend beyond the surface if it were not deflected by thatsurface to anextent equal to three-eighths of the length of the bristlesclear of the ferrule. The brush and holder is weighed.'The brush isdipped into the paint to a depth equal to one-half the length of bristleclear of the ferrule for 3:0.1 minutes. The brush is then raised andallowed to drip for 60- seconds and the brush and holder then reweighed.With paper in place the brush is placed in the painting machine and thebrush allowed to paint for a total of 60, 35-inch strokes changing paperevery 20 strokes. The brush and holder is reweighed. The brush isredipped in the paint to the same depth as above, but for 30 seconds,allowed to drip for 30 seconds, and the above painting and weighingprocedure repeated. This last procedure is repeated until fiveconsecutive runs have a range of 2.0 g or less, or until 15 values havebeen obtained. The figures reported are averages of these values.

The dump", is determined by the samestarting procedure as in the paintrelease test by dipping the brush into the paint to a depth equal toone-half the length of the bristle clear of ferrule for 310.1 minutes.

seconds. The brush is then placed in the painting machine and a blackMorest form 4 inches wide and only 4% inches long is painted with onestroke, and the cardboard form then weighed. The dump" is the amount ofpaint delivered onto the 4 X4% inch'form in this first stroke.

fCovering ability is determined with a brush which has just completedthe paint release test by dipping it in the paint in the standard mannerfor 30 seconds, raising it and allowing it to drain for 30 seconds.

A black Morest Co. form (35 inches long and 4 inches wide) is placed inthe painting machine at the middle of the painting patch of the brushand the cardboard form painted using the number of strokes required tocompletely cover the panel up to a minimum of six strokes. The Morestform is removed and allowed to dry. Without redipping the brush,additional Morest forms are completely covered. The test is repeatedfour more times. When the paint has dried, the number of square inchesof area covered by the brush after each of the five dips is determined.Any squares which have any uncovered black surface are excluded from thecount. The average of the four covering ability values which gives thesmallest range of paint containing 37 percent pigment and 63 percentvehicle, in which the pigment consists of 50 percent titanium dioxideand 50 percent silicates, and the vehicle consists of 23 percent ofnon-volatile (petroleum) latex and 77 percent water, the brush exhibitsa dump of 4.9 grams, a paint release of 21.4 grams, and'a coverage of304 square inches. All percentages are given by weight.

The 4-inch brush has a stiffness of 815 grams as measured by pressingthe tips of the bristles of the brush while being held at 10 fromvertical against the horizontal pan of a balance at a distance to causea deflection of the bristles equal to three-eighths the length of thebristles as measured from their tips to the ferrule of the brush.

EXAMPLEIII Example I is repeated except using poly(butylene-1,4-terephthalate) flake having an inherent viscosity of 0.8 as measuredfrom a 0.5 percent solution in 40/60 tetrachloroethane and phenol and ahot water bath maintained at 80 C is used as the drawing assist ratherthan the hot air tubular furnace.

EXAMPLE [11 Example I is repeated except the surface of thepoly(butylene-1,4-terephthalate) flake is surface coated with 0.3 weightpercent of brown acid dye. The

bristle tips and flags similarly to the bristles formed by Example I. vI

EXAMpLE IV sweep to dry the flake. The flake is then charged to a 1%inch single screw extruder' arranged with its discharge coupled directlyto the intake of a metering gear pump. The melted polymer'in theextruder is maintained at 240 C. The gear pump forces the melted polymerthrough a screen pack and breaker plate assembly and then though aspinneret having 14 holes 30 mils in diameter. Discharge from thespinneret is vertically downward into a cold water quench bathmaintained at 25 C. The surface of the water isabout onehalf inch belowthe spinneret. The take-off arrangement employs rubber pinch rolls whichare operated at a constant speed to produce filaments having a diameterof 10 mils. These filaments are then drawn 4X with a conventional slowroll-fast roll arrangement using a short water bath maintained at "--Cbetween the slow roll and fast roll as a draw assist and approximatelya1- second contact time in the water bath.

The filament is wound up on a spool. In a separate operation thefilaments'are placed between clamps 62 cm apart and the separationadjusted for a 10 percent relaxationfThe assembly is then placed in anair oven maintained at C for 30 seconds.

The physical properties of the filaments are determined by the followingmethods on filament stored at 23 C and 50 percent relative humidity forat least 2 days after the hot air conditioning. The tensile strength fora filament having a diameter (D) in inches and a break load (BL) inpounds as measured on an lnstron Universal Tensile Tester using a10-inch gap and drawing at 10 inches per minute at 23 C and 50 percentRH is calculated by the following equation:

Tensile strength (in psi) 4BL/1i-D I Ultimate elongation is determinedfrom the lnstron chart by dropping a perpendicular from the break pointto the time axis of the chart, then measuring the distance (6'') alongthe time axis from the point where said perpendicular hits the axis tothe beginning of the load-time curve, calculating ultimate elongation bythe following equation wherein L is the initial gauge length in inchesand m is a chart magnification that is the ratio of chart speed to crosshead speed Ultimate elongation (in percent) l00C'/Lm Tensile modulus isalso determined in an lnstron Universal Tensile Tester using a 10-inchgap and drawing at 1 inch per minute at 23 C and 50 percent RH and iscalculated by the following equation wherein C is distance on thelnstron Chart in inches and P is the load in pounds at that point:

Tensile modulus (in psi) 4PmL/D C wraps, waiting 4 minutes and thencutting the monofilament off the mandrel and placing the filament inwater at 23 C and allowing it to relax for 1 hour and again noting thenumber of loops after recovery. The percent recovery is calculated fromthe following equation:

the filament has a wet tensile. modulus of psi determined as describedabove except the filament is 7 tested after immediate removal fromdistilled water. The sample has been previously immersed for 48 hours inwater. This represents a tensile modulus ratio wet/dry of 0.91. Tensilemodulus is measured here because it is easily determined accuratelywhile the flexural modulus which measures stiffness is difficult toobtain with any degree of accuracy. Both of these moduli are known to benearly equal on materials of this type, and thus tensile modulus is usedfor convenience; I i

late) flake having an inherent viscosity of-0.97 as measured from a 0.5gsolution in 100 ml of 40/60 tetrachloroethane/phenol is used, and a4.1X draw is used followedby a l.3 draw using a Ucon oil SOHB260, apolyalkylene glycol bathat 115 C as the assist to give an overall drawratio of 5.35X. The filament is heat set at l90 C at constant lengthwith a 60- seconds residence time. The filament has a tensile modulus of593,000 psi, a tensile strength of 82,500 psi, an ultimate elongation of23 percent, a mandrel bend recovery of 92 percent, and a wet tensilemodulus of 567,000 psi, thus representing a modulus ratio wet/dry of0.96. The test results reported in the Example are determined by thetests described in Example IV.

EXAMPLE VI used, an extruder melt temperature of 270 C is used,

and the water bath is maintained at 80 C. Brushes made from thesebristles which have been tipped and flagged as in Example I are found toexhibit outstanding painting qualities along with exceptionaldurability.

EXAMPLE VII Example I is repeated except poly(butylene-l,4-terephthalate) prepared in accordance with the teachings of U.S. Pat.No. 3,405,098, and having an inherent viscosity of 1.2 as measured froma 0.5 g solution in 100 ml of 40/60 tetrachloroethane/phenol is used, anextruder melt temperature of 270 C is used and the water bath ismaintained at 80 C. The bristles are tipped by the procedures of ExampleI but not flagged. A 4-inch brush is made up from these tipped but notflagged filaments, which are then microflagged as follows: A 12-inchdiameter metal plate onehalf inch thick is attached at its center to ashaft which can be rotated at 3,450 rpm. by an electric motor. At theouter edge of the steel plate three hardened cap screws are screwed intoholes and extendout 1% inches at right angles to the plane of thecircular steel disk. These cap screws are A-inch diameter and have aconventional screw thread. The circular etal disk with its pro ectingcap screws 18 then rotate at 3,4 0 r.p.m.

The paint brush is then inserted through a guard and the ends of thepaint brush bristles are struck by the sides of the threaded -cap screws(with the axis of the screws at right angles to the axis of thebristles). The brush is held against the rotating cap screws for a totalof 30 seconds while striking one side only of the flat side of the l X 4inch wide brush from which the bristles extend 3% inches. The.difference in the appearance of thebristles is dramatic for thepoly(butylene-l,4terephthalate) after the 30-second treat-- ment.

Themicroflagging" produces very fine diameter microhairlike ends ascompared with the more conventional flagging which is produce bysplitting the ends of the bristles with sharp rotating knife disks withthe plane of the disk parallel to the axis of the bristles. Aftermicroflagging, the end of'the bristle generally has from 10-20 of thesemicrohair divisions for each poly( butylene-l ,4-terephthalate) bristle.

This brush exhibits superior painting qualities.

We claim:

1. An article of manufacture comprising oriented, heat-set bristles of alength suitable for use in a paint brush, the bristles'having a minimumdiameter of 3 mils and being composed ofpoly(butylene-l,4-terephthalate) having an inherent viscosity of fromabout 0.5 to about L5 as measured froma 0.5 g. solution in 10 0 ml. of asolvent consisting of 40 percent tetrachloroethane and 60 percentphenol.

2. The article of claim 1 wherein the, bristles are tipped and flagged.

3. The article of claim 2 wherein the bristles are tapered and have abase from 6 to 20 mils in diameter and a minimum diameter from 0.5 to0.75 the diameter of the base.

4. The article of claim 3 wherein the bristles have been microflagged toproduce about l0-20 microhair divisions at the tipped end of thebristles.

5. A paintbrush comprising oriented, heat-set bristles ofpoly(butylene-l,4-terephthalate) having a minimum diameter of 3 mils andan inherent viscosity of from about 0.5 to about 1.5, as measured from a0.5 g. solution of a solvent consisting of 40 percent tetrachloroethaneand 60 percent phenol.

6. The paint brush of claim 5 wherein the bristles are tipped andflagged.

7. The paint brush of claim 5 wherein the bristles are tapered and havea maximum diameter in the range of 6 to 20 mils and a minimum diameterin the range of 3 to 15 mils.

8. The paint brush of claim 6 wherein the bristles have beenmicroflagged to produce about 10-20 microhair divisions at the tippedend of the bristles.

* I a F

2. The article of claim 1 wherein the bristles are tipped and flagged.3. The article of claim 2 wherein the bristles are tapered and have abase from 6 to 20 mils in diameter and a minimum diameter from 0.5 to0.75 the diameter of the base.
 4. The article of claim 3 wherein thebristles have been microflagged to produce about 10-20 microhairdivisions at the tipped end of the bristles.
 5. A paintbrush comprisingoriented, heat-set bristles of poly(butylene-1,4-terephthalate) having aminimum diameter of 3 mils and an inherent viscosity of from about 0.5to about 1.5, as measured from a 0.5 g. solution of a solvent consistingof 40 percent tetrachloroethane and 60 percent phenol.
 6. The paintbrush of claim 5 wherein the bristles are tipped and flagged.
 7. Thepaint brush of claim 5 wherein the bristles are tapered and have amaximum diameter in the range of 6 to 20 mils and a minimum diameter inthe range of 3 to 15 mils.
 8. The paint brush of claim 6 wherein thebristles have been microflagged to produce about 10-20 microhairdivisions at the tipped end of the bristles.